合法域名校验错误

function isValidDomain(domain) {
    const domainRegex = /^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,6}$/;
    return domainRegex.test(domain);
}

console.log(isValidDomain("example.com")); // true
console.log(isValidDomain("example")); // false

const dns = require('dns');

function checkDomainResolution(domain, callback) {
    dns.resolve4(domain, (err, addresses) => {
        if (err) {
            console.error(`DNS resolution failed for ${domain}:`, err);
            callback(false);
        } else {
            console.log(`DNS resolved for ${domain}:`, addresses);
            callback(true);
        }
    });
}

checkDomainResolution("example.com", (isValid) => {
    console.log(`Domain is valid: ${isValid}`);
});

const dns = require('dns');

function checkDomainExistence(domain, callback) {
    dns.resolveMx(domain, (err, addresses) => {
        if (err) {
            console.error(`Domain does not exist: ${domain}`, err);
            callback(false);
        } else {
            console.log(`Domain exists: ${domain}`, addresses);
            callback(true);
        }
    });
}

checkDomainExistence("nonexistentdomain.com", (exists) => {
    console.log(`Domain exists: ${exists}`);
});